C2 certainly holds off the reset, not sure if it's just for pwdn, or also startup. If you can check voltages around the reset logic,
might give you some more clues. Not much else I can think of that could be causing this, although I suppose if you have enough ripple
on the +5v to the microprocessor, that could be triggering its own shutdown/restart. But, you've already checked that.
PS - my comment about the nvram was for the 'cal constant' thread. I just combined them. Guess I should have pointed that out. :)
BTW, my 7081 that usually holds calibration very well was off by 10 ppm when I turned it on a few days ago even after 24h warmup.
Hope this isn't a sign of something bad coming. I have an HP 3458 ref, maybe I'll try that mod to use it in my 7081.
Interestingly, my 7061 has held calibration impressively, off by only 3 ppm, and it's been a year since I calibrated it.
(I use a pair of Datron 4910's for calibration. I had one calibrated by Fluke, and I do differential comparisons between the two
to track drift. They are amazingly stable. Of course, they have been in continuous operation for about 12 years in my lab, and who
knows how long before I got them.)
-----Original Message-----
Hi Bill,
C2 is a hermetic tantalum, and doesn't appear leaky. +5V appeared on the mark and stable but C60 (220uF 10V in +5V supply) looked a bit crusty, so I replaced it on general principle with a 220uF 10V tant.
I think that C2 is used to hold off of the reset signal for a period of time after PWDN- is asserted to allow the processor to save stuff to RAM.
The ROMS appear all good and were all written pretty recently.
Dave
--
Bill Ezell
----------
The day Microsoft makes something that doesn't suck
will be the day they make vacuum cleaners.
Or maybe Windows 10.